1. Field of the Invention
The present invention relates to high-frequency modules, and particularly, to a high-frequency module including a surface acoustic wave device or a boundary wave device.
2. Description of the Related Art
Conventionally, high-frequency modules including a surface acoustic wave filter are used in mobile phones and other suitable devices.
For example, a high-frequency module 1, as illustrated in an electric circuit diagram in FIG. 16 and a perspective view in FIG. 17, includes an inductor 4 that is arranged across balanced output terminals 3a and 3b of a surface acoustic wave element 3 on a top surface of an insulating substrate 2, the surface acoustic wave element 3 and the inductor 4 are connected through connection lines 5 provided on the top surface of the insulating substrate 2, and a terminal of the inductor 4 and a connection terminal (not shown) are provided on the bottom surface of the insulating substrate 2 and connected by a via-hole conductor (not shown) in the insulating substrate 2 (See, for example, Japanese Unexamined Patent Application Publication No. 2003-142981).
When the configuration of the conventional art described above is used, for example, a high-frequency module 10a in which a plurality of surface acoustic wave filters 18 and inductors 16 are mounted on a top surface 13a of an insulating substrate 13 may be provided, as illustrated in a perspective view in FIG. 8, a cross-sectional view in FIG. 9, an exploded perspective view in FIG. 10, and a perspective view of insulating substrate top and bottom surfaces in FIGS. 11A and 11B.
In this case, as illustrated in FIG. 9 and FIGS. 11A and 11B, mounting lands 34 for mounting the inductors 16, and connection terminals 26 on a bottom surface 13b of the insulating substrate 13 are respectively connected to opposite ends of via-hole conductors 44. Thus, the pitch Pa of the mounting lands 34 for mounting the inductors 16 and the pitch of the connection terminals 26 on the bottom surface 13b of the insulating substrate 13 must be substantially equal.
Meanwhile, for high-frequency modules for mobile phones and other suitable devices, a reduced size and a decrease in the pitch of connection terminals are required.
To decrease only the pitch of connection terminals, as in a high-frequency module 10b illustrated in a perspective view in FIG. 12 and a perspective view in FIG. 13 of an insulating substrate bottom surface viewed from the top surface side, extension portions 37 extending from the mounting lands for mounting inductors are provided on a top surface 14a of an insulating substrate 14, and via-hole conductors are provided downward from the extension portions 37, so that a pitch Pb of connection terminals 28 on the bottom surface 14b of the insulating substrate 14 may be decreased. In this case, an extra space 14x for providing the extension portions 37 is required on the insulating substrate 14. This causes an increase in the dimensions of the product, and thus has adverse effects on the reduction in size of high-frequency modules.
To decrease the pitch of connection terminals while maintaining a reduced product size, as in a high-frequency module 10c illustrated in a perspective view in FIG. 14, a plan view in FIG. 15A of an insulating substrate top surface, and a perspective view in FIG. 15B of an insulating substrate bottom surface viewed from the top surface side, the size of elements 17 to be mounted on a top surface 15a of an insulating substrate 15 may be decreased. In this case, it is necessary to select the elements 17 having a size suitable for the pitch of connection terminals 27 on a bottom surface 15b of the insulating substrate 15. Thus, a pitch Pc of the connection terminals 27 is restricted by the size of the elements 17. In addition, there is a limitation in the manufacturing technique for decreasing a distance between via-hole conductors. Therefore, the pitch Pc of the connection terminals 27 can only be decreased to a certain extent.